From 693565ddda56295845f92f8290ebb2a2b64be9f5 Mon Sep 17 00:00:00 2001
From: Ilya Puchka <ilyapuchka@gmail.com>
Date: Sat, 12 Jan 2019 22:10:21 +0000
Subject: [PATCH] syntax error on empty variable tag

---
 CHANGELOG.md                             | 4 ++++
 Sources/Extension.swift                  | 2 +-
 Sources/Node.swift                       | 5 ++++-
 Tests/StencilTests/EnvironmentSpec.swift | 7 ++++++-
 4 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 558e8cd..4f87233 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,10 @@ _None_
   [Ilya Puchka](https://github.com/ilyapuchka)
   [#254](https://github.com/stencilproject/Stencil/pull/254)
 
+- Throw syntax error on empty variable tags (`{{ }}`) instead `fatalError`.  
+  [Ilya Puchka](https://github.com/ilyapuchka)
+  [#263](https://github.com/stencilproject/Stencil/pull/263)
+
 ### Internal Changes
 
 - `Token` type converted to struct to allow computing token components only once.  
diff --git a/Sources/Extension.swift b/Sources/Extension.swift
index e994e6e..a91b4ab 100644
--- a/Sources/Extension.swift
+++ b/Sources/Extension.swift
@@ -89,7 +89,7 @@ enum Filter: FilterType {
     switch self {
     case let .simple(filter):
       if !arguments.isEmpty {
-        throw TemplateSyntaxError("cannot invoke filter with an argument")
+        throw TemplateSyntaxError("Can't invoke filter with an argument")
       }
       return try filter(value)
     case let .arguments(filter):
diff --git a/Sources/Node.swift b/Sources/Node.swift
index 8885ff6..d06d3ca 100644
--- a/Sources/Node.swift
+++ b/Sources/Node.swift
@@ -84,7 +84,10 @@ public class VariableNode: NodeType {
       elseExpression = nil
     }
 
-    let filter = try parser.compileResolvable(components[0], containedIn: token)
+    guard let resolvable = components.first else {
+      throw TemplateSyntaxError(reason: "Missing variable name", token: token)
+    }
+    let filter = try parser.compileResolvable(resolvable, containedIn: token)
     return VariableNode(variable: filter, token: token, condition: condition, elseExpression: elseExpression)
   }
 
diff --git a/Tests/StencilTests/EnvironmentSpec.swift b/Tests/StencilTests/EnvironmentSpec.swift
index 2acfa30..f1bf469 100644
--- a/Tests/StencilTests/EnvironmentSpec.swift
+++ b/Tests/StencilTests/EnvironmentSpec.swift
@@ -133,6 +133,11 @@ final class EnvironmentTests: XCTestCase {
         token: "name|unknown"
       )
     }
+    
+    it("reports error in variable tag") {
+      self.template = "{{ }}"
+      try self.expectError(reason: "Missing variable name", token: " ")
+    }
   }
 
   func testRenderingError() {
@@ -153,7 +158,7 @@ final class EnvironmentTests: XCTestCase {
 
     it("reports passing argument to simple filter") {
       self.template = "{{ name|uppercase:5 }}"
-      try self.expectError(reason: "cannot invoke filter with an argument", token: "name|uppercase:5")
+      try self.expectError(reason: "Can't invoke filter with an argument", token: "name|uppercase:5")
     }
 
     it("reports rendering error in custom tag") {